Multi-layer tube of a muffler for an internal combustion engine

ABSTRACT

A tube of a muffler for an internal combustion engine includes at least two generally rectangular sheets which are joined together at one end by crimping and wound in a tubular configuration to constitute two consecutive layers. In the tubular configuration, the other end of each of the two sheets overlaps the sheet itself and welded to the latter straddling a coupling portion where the two sheets are joined. While one of the sheets which constitutes an inner layer of the tube is made of a material which is resistive to corrosion due to chemical reactions with combustion gas and others flowing through the tube, the other which constitutes an outer wall of the same is made of a material which withstands adverse ambient conditions such as briny air and high humidity.

This application is a divisional of copending application Ser. No.919,499, filed on Oct. 2, 1986, now U.S. Pat. No. 4,793,544.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a muffler for use with an internalcombustion engine and, more particularly, to a multi-layer tube of themuffler and a method of producing the same.

2. Description of the Prior Art

A tube of a muffler for use with an internal combustion engine issusceptible to corrosion on both the inner and outer surfaces thereof.Specifically, corrosion of the inner surface is caused by chemicalreactions with water condensed in and entrained by exhaust gas and witha catalyst adapted for exhaust emission control, while corrosion of theouter surface is brought about by briny air, high humidity and otherenvironment conditions under which a muffler is often used. That is, thecause of corrosion differs from the inner surface to the outer surfaceof the tube.

There has been proposed a tube for an automotive muffler having aplurality of concentric layers which are individually made of particularmaterials matching the different causes of corrosion as stated above, asdisclosed in Japanese Patent Laid-Open Publication No. 83622/1982. Theprior art multi-layer muffler is produced by laying a sheet of stainlesssteel on a sheet of aluminum-plated steel and, then, directly rollingthe two sheets together. In detail, such a muffler is produced bywinding the two sheets made of different materials at least one turn byrolling. The production, therefore, requires a considerable compressionforce for winding which has to be implemented with a highly rigidrolling machine. Further, it is necessary for the two blanks to bepositioned with extreme care so as not to be dislocated relative to eachother.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a tube ofa muffler for an internal combustion engine which eliminates theabove-discussed drawbacks and can be produced with efficiency.

In accordance with the present invention, there is provided asubstantially cylindrical tube of a muffler for use with an internalcombustion engine comprising a generally rectangular first sheet whichis wound in a tubular configuration such that the sheet overlaps itselfpartially, and a generally rectangular second sheet having end portionswhich extend in an axial direction of the tube and one of which isjoined by crimping with one end portion of the first sheet which extendparallel to the axial direction of the tube. The second sheet is woundon an outer periphery of the first sheet in a tubular configuration suchthat the second sheet partially overlaps itself straddling a portionwhere the first and second sheets are jointed by crimping. The firstsheet is dimensioned in a circumferential direction of the tube suchthat the other end portion overlaps a portion of the first sheet whichis wound in the tubular configuration. The second sheet is dimensionedin a circumferential direction of the tube such that the other endportion overlaps a portion of the second sheet which is wound in thetubular configuration, the overlapping portions being welded together.

In accordance with the present invention, there is also provided asubstantially cylindrical tube of a muffler for use with an internalcombustion engine comprising a generally rectangular first sheet whichis wound in a tubular configuration such that the sheet overlaps itselfpartially, a generally rectangular second sheet having end portionswhich extend in an axial direction of the tube and one of which isjoined by crimping with one of end portions of the first sheet whichextend parallel to the axial direction of the tube, the second sheetbeing wound on an outer periphery of the first sheet in a tubularconfiguration such that the second sheet partially overlaps itselfstraddling a portion where the first and second sheets are joined bycrimping, and a generally rectangular third sheet having end portionswhich extend parallel to the axial direction of the tube and one ofwhich is joined by crimping with the other end portion of the secondsheet. The third sheet is wound on an outer periphery of the secondsheet in a tubular configuration such that the third sheet partiallyoverlaps itself straddling a portion where the second and third sheetsare joined by crimping. The first sheet is dimensioned in acircumferential direction of the tube such that the other end portion ofthe first sheet overlaps a portion of the first sheet which is wound inthe tubular configuration. The second sheet is dimensioned in thecircumferential direction of the tube such that the other end portion ofthe second sheet overlaps a portion of the second sheet which is woundin the tubular configuration. Further, the third sheet is dimensioned inthe circumferential direction of the tube such that the other endportion of the third sheet overlaps a portion of the third sheet whichis wound in the tubular configuration, the overlapping portions beingwelded together.

In accordance with the present invention, there is further provided amethod of producing a substantially cylindrical tube of a muffler foruse with an internal combustion engine comprising the steps of preparingfirst and a second generally rectangular sheets each of which isdimensioned in a circumferential direction of the tube such that one ofthe end portions of the sheet which are parallel to an axial directionof the tube overlaps a portion of the sheet which is wound in a tubularconfiguration, joining the other end of the first and second sheets bycrimping, inserting the one end portion of the first sheet in a slot ofa mandrel which extends parallel to an axial direction of the mandrel,driving the mandrel in a rotational motion while pressing a rollertoward the mandrel against the first and second sheets which aresequentially wrapped around the periphery of the mandrel in a tubularconfiguration, whereby the first sheet is wound in a tubularconfiguration such that the first sheet overlaps with the one endportion thereof, and the second sheet is wound in a tubularconfiguration on the outer periphery of the first sheet such that oneend portion of the second sheet overlaps the second sheet, and weldingthe second sheet and the one end portion thereof which overlap eachother.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven way of illustration only, since various changes and modificationswithin the spirit and scope of the invention will become apparent tothose skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from the consideration of the following detailed descriptiontaken in conjunction with the accompanying drawings which are given byway of illustration only, and thus, are not limitative of the presentinvention, and in which:

FIG. 1 is a side elevation showing an embodiment of a muffler for aninternal combustion engine to which the present invention is applied;

FIG. 2 is a section along line II--II of FIG. 1, showing a tube of themuffler;

FIG. 3 is a side elevation showing blanks in one of steps of producingthe tube of FIG. 2;

FIG. 4 is a schematic view representative of a wraping step inaccordance with the same embodiment;

FIG. 5 is a view similar to FIG. 2, showing a three-layer tube inaccordance with an alternative embodiment of the present invention;

FIG. 6 is a fragmentary section of a three-layer tube in accordance withstill another embodiment of the present invention; and

FIG. 7 is a side elevation of blanks in one of the steps of producingthe tube of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, a muffler for an internalcombustion engine to which the present invention is applied is shown andgenerally designated by the reference numeral 10. As shown, the muffler10 is connected at one end to an exhaust pipe 12 and at the other end toa tail pipe 14. The muffler 10 comprises a tubular body, or tube, 16.

As shown in FIG. 2, the tube 16 is made up of two sheets 18 and 20 whichare configured in a multi-layer structure. One of the sheets, e.g., thesheet 18 is made of stainless steel which is resistive to combustion gasand condensed water derived from the combustion gas, which flow throughthe tube 16. The other sheet, i.e., the sheet 20 in this example is madeof steel which is treated for resistively against briny air as typifiedby an aluminum- or zinc-plated steel sheet. Depending upon the situationin which the muffler 10 is used and the conditions surrounding themuffler 10, the aluminum- or zinc-plated steel sheet may be applied tothe sheet 18, which defines the inner wall of the muffler 10, and thestainless steel sheet to the sheet 20 which defines the outer wall ofthe same.

In this particular embodiment, the tube 16 has a substantially circularcross-section. As shown in FIG. 2, one widthwise end of the sheet 18,i.e., one end which extends in an axial direction A of the tube 16, FIG.1, is connected to the sheet 20 by crimping to constitute a couplingportion 22. The other end portion 24 of the sheet 18 overlaps and iswelded to the sheet 18 itself. Likewise, the other end portion 26 of theother sheet 20 overlaps and is welded to the sheet 20 itself. In thismanner, the tube 16 of the muffler 10 is provided with a generallycylindrical configuration. Where the coupling portion 22 is dimensioned,for example, 10 millimeters as measured in the circumferentialdirection, it is preferable that each of the overlapping portions 24 and26 of the sheets 18 and 20 be about 15 to 20 millimeters long.

The muffler 10 having the above construction is produced as follows.First, as shown in FIG. 3, a pair of generally rectangular sheet blanks18a and 20a are each bent, or crimped, in a U-shape at one end thereof,then mated together along the U-bends, and then pressed together. As aresult, the blanks 18a and 20a are joined to each other by the couplingportion 22 to form a single elongate sheet, generally 16a. Because theblanks 18a and 20a are different from each other in material, it isgenerally difficult to weld them together. While spot-welding orfull-surface welding may be positively employed to connect the blanks18a and 20a along the coupling portion 22, the former technology wouldinvite leakage of exhaust gas through the coupling portion 22 and thelatter would result in the need for a substantial number of extra stepsand substantial power and, therefore, disproportionate cost. Incontrast, the crimping type connection as stated above is easy toperform and inexpensive and, moreover, ensures a sufficient sealingability against exhaust gas.

Assume that the blank 18a is to constitute the inner tube part 18 by wayof example. As shown in FIG. 4, the free end 24a of the blank 18a isinserted into, for example, a slot 50 which is formed in a mandrel 52.Then, the mandrel 52 is rotated in a direction indicated by an arrow L₁while, at the same time, a pressure roller 54 located adjacent to themandrel 52 is pressed against the mandrel 52, thereby wrapping the blank18a around the mandrel 52. The blank 18a is dimensioned such that itoverlaps itself over a predetermined length 24 after one turn around themandrel 52.

When the blank 18a has overlapped itself over the length 24 after oneturn around the mandrel 52 as stated above, it forms the entire innerperiphery of the inner tube part 18. The overlapping portion 24 of theblank 18a may be welded at this stage of production. As the mandrel 52is further rotated, the other blank 20a is wrapped around the blank 18a.The wrapping operation is completed when the free end 26a of the blank20a has overlapped the blank 20a itself over a predetermined length 26straddling the coupling portion 22.

Under the condition described above, an electrode 58 provided in a partof the outer periphery 56 of the mandrel 52 and an electrode 60 disposedabove the periphery 56 of the mandrel 52 are activated to spot-weld theoverlapping portion 26 of the blank 20a. The substantially cylindricaltube 16 is completed by such a procedure and, then, removed from themandrel 52. It is to be noted that welding the blank 20a at theoverlapping portion 26 is easy since the blank 20a is made of a singlematerial.

Referring to FIG. 5, another embodiment of the present invention isshown. In FIG. 5, the same or similar structural elements as those shownin FIG. 2 are designated by like reference numerals. As shown, the tube16 of FIG. 5 has a three-layer structure made up of the inner and outertube parts 18 and 20 plus an intermediate buffer layer 30. Specifically,the buffer layer 30 which may be made of a sound absorbent material, forexample, is laid between the tube parts 18 and 20 by applying it to thatsurface of the blank 20a which is to constitute the inner surface, i.e.,underside while the blank 20a is wrapped around the mandrel 52.

FIG. 6 shows still another embodiment of the present invention whichalso employs a three-layer structure. In FIG. 6, the same or similarstructural elements as those shown in FIG. 5 are designated by likereference numerals. In the tube 16 of FIG. 6, both the inner and outersheets 18 and 20 are made of a corrosion resisting material such asstainless steel. Interposed between the sheets 18 and 20 is a sheet 32which comprises, for example, SPCC (plain steel sheet). This kind ofstructure minimizes the amount, inclusive of length and thickness, ofthe highly corrosion resisting and expensive material 18 and 20 which isnecessary for the tube 16 to be completed. However, simply providing theinner and outer tubes 18 and 20 would bring about problems such astransmission of exhaust noise through the tube 16 due to their shortthickness. Such problems can be advantageously solved by using the steelsheet 32 which is inexpensive and sufficiently thick.

As shown in FIG. 7, the three-layer tube 16 of FIG. 6 consists of threeblanks 18a, 32a and 20a which are joined together at coupling portions22a and 22b by crimping. The resultant sheet 16a is rolled and welded aspreviously described. It is to be noted that the crimped portions 22aand 22b of the sheet 16a may each be configured convex either outwardlyof the tube 16 to be produced, i.e., upwardly as viewed in FIG. 7 orinwardly of the same, i.e., downwardly as desired. Further, even a tubehaving four or more layers may advantageously be produced by the samemethod as the three-layer tube.

The rolling process as previously stated may be implemented with amandrel having a fixed diameter, which corresponds to that of aparticular tube 16 to be produced, and a pressure roller cooperativewith the mandrel. This, however, results in a prohibitive equipment costwhen it is desired to produce tubes 16 having various diameters.

Another possible implementation for the production of tubes 16 having awide range of diameters is using a pressure roller made of urethane foamand other elastic materials as the roller 54, FIG. 4, together with asingle mandrel having a predetermined diameter. The elastic roller 54 isto effectively utilize spring-back of the sheet 16a which has underwentwrapping operation. The mandrel 50 may advantageously be implementedwith one having a fixed diameter and made of iron, for example. Thesheet 16a is wound around the mandrel 50 while being nipped between themandrel and the urethane roller, the urethane roller being pressedagainst the mandrel to provide the sheet 16a with a tubularconfiguration. Subsequently, the tubular sheet 16a is removed from themandrel and then fixed to a desired diameter, followed by spot-weldingor otherwise rigidly joining the overlapping portion 26.

In accordance with the above-described procedure, the roller iselastically deformable so that the tube 16 may be provided with anydesired diameter by adjusting the pressure force which acts between theelastic roller and the mandrel. Alternatively, a collar of a desireddiameter, not shown, may be applied to the outer periphery of a mandrelwhich has a fixed diameter and driven by the mandrel for rotation, thesheet 16a being inserted between the collar and the pressure roller. Allof these methods eliminate the need for mandrels each having aparticular diameter and, thereby, cut down the equipment cost.

In summary, it will be seen that in accordance with the presentinvention there is provided a multi-layer tube which is simple instructure and highly resistive to corrosion on both of the inner andouter surfaces thereof. The tube is positively sealed in spite of thesimple structure and produced by substantially the same principle as aprior art tube which is a roll of a single sheet. It will be needless tomention that the present invention is effectively applicable not only toa tube having a circular cross-section but to those having oval andother smooth cross-sections.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by thoseembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodiments

without departing from the scope and spirit of the present invention.

What is claimed is:
 1. A substantially cylindrical tube for a mufflerfor use with an internal combustion engine, comprising:a generallyrectangular first sheet having end portions, said first sheet beingwound in a tubular configuration such that said sheet overlaps itselfpartially; and a generally rectangular second sheet having end portionswhich extend in an axial direction of said tube and having one endportion joined by crimping with one end portion of said first sheetwhich extends parallel to said axial direction of said tube, said secondsheet being wound on an outer periphery of said first sheet in a tubularconfiguration such that said second sheet partially overlaps itselfstraddling a portion where said first and second sheets are joined bycrimping; said first sheet being dimensioned in a circumferentialdirection of said tube such that the other end portions overlaps aportion of said first sheet which is wound in the tubular configuration;said second sheet being dimensioned in a circumferential direction ofsaid tube such that the other of said end portions overlaps a portion ofsaid second sheet which is wound in the tubular configuration, saidoverlapping portions being welded to each other; whereby said tube witha substantially cylindrical configuration is formed.
 2. A tube inaccordance with claim 1, wherein said first sheet comprises a steelsheet which is plated with a material selected from the group consistingaluminum and zinc.
 3. A tube in accordance with claim 1, wherein saidfirst sheet comprises a steel sheet which is plated with a materialselected from the group consisting of aluminum and zinc, said secondsheet comprising a stainless steel sheet.
 4. A tube in accordance withclaim 1, wherein said overlapping portions of said second sheet arespot-welded to each other.
 5. A tube in accordance with claim 1, furthercomprising a generally rectangular third sheet which includes a soundabsorbent material and is wound between said first and second sheets. 6.A substantially cylindrical tube for a muffler for use with an internalcombustion engine, comprising:a generally rectangular first sheet havingend portions, said first sheet being which is wound in a tubularconfiguration such that said sheet overlaps itself partially; agenerally rectangular second sheet having end portions which extend inan axial direction of said tube and having one end portion joined bycrimping with one of end portion of said first sheet which extendparallel to said axial direction of said tube, said second sheet beingwound on an outer periphery of said first sheet in a tubularconfiguration such that said second sheet partially overlaps itselfstraddling a portion where said first and second sheets are joined bycrimping; and a generally rectangular third sheet having end portionswhich extend parallel to said axial direction of said tube and havingone end portion joined by crimping with the other of said end portionsof said second sheet, said third sheet being wound on an outer peripheryof said second sheet in a tubular configuration such that said thirdsheet partially overlaps itself straddling a portion where said secondand third sheets are joined by crimping; said first sheet beingdimensioned in a circumferential direction of said tube such that theother end portion of said first sheet overlaps a portion of said firstsheet which is wound in the tubular configuration; said second beingdimensioned in said circumferential direction of said tube such thatsaid other end portion of said second sheet overlaps a portion of saidsecond sheet which is wound in the tubular configuration; said thirdsheet being dimensioned in said circumferential direction of said tubesuch that the other of said end portions of said third sheet overlaps aportion of said third sheet which is wound in the tubular configuration,said overlapping portions being welded to each other; whereby saidsubstantially cylindrical tube is formed.
 7. A tube in accordance withclaim 6, wherein said first and third sheets are made of stainlesssteel, and said second sheet is made of plain steel.